It is known that when a beam of electromagnetic radiation is caused to impinge on the surface of a transparent or semi-transparent sample at an oblique or normal angle, reflected electromagnetic radiation from said sample generally contains components not only from the incident surface thereof, but also from the opposite, back, surface thereof. Especially where a sample investigated is anisotropic, the effect of said opposite, back, surface reflections can be difficult to model, and this makes characterization of the sample, or surface films thereupon, far more difficult, even essentially impossible. It is therefore desirable to reduce or eliminate the presence of said opposite, back, surface reflections while detecting electromagnetic radiation which reflects from an incident, front, surface thereof. It is disclosed that the identified problem can be present in systems where an anisotropic sample is elongated, such as a ribbon or sheet, and is continuously pulled over the means for supporting a sample, or in fixed position samples. Where said anisotropic sample and means for supporting it have different refractive indicies, opposite, back, surface reflections develop.
No known prior art addresses the problem where anisotropic samples are involved, however, regarding isotropic samples known approaches to reducing the problems caused by opposite, back, surface reflections generally include:                mitigating opposite surface reflections by spatially separating said opposite, back, surface from the incident surface of a sample, (ie. use thick samples);        the use a wedge shaped sample;        roughen the opposite surface of the sample, (which it is noted is destructive and difficult on thin, brittle or soft samples), so that electromagnetic radiation incident thereupon is scattered rather than specularly reflected therefrom; and        provide sample index matched material at said opposite, back, surface;        account for opposite surface reflections via mathematical modeling.        
It is noted that separating the incident (front) and opposite (back) surfaces of a sample does not work well if the diameter of the electromagnetic beam used in the sample investigation is larger than is the sample thickness. Focusing of a beam is, of course, possible to reduce its diameter at the point where it impinges on a sample, but this introduces a spread in the angle of incidence, which angular spread adds complexity and should be accounted for in a mathematical model of the sample. It is noted that accounting for opposite surface reflections via mathematical modeling introduces complexity into the model, and this is particularly troublesome where a sample is anisotropic in that different indicies of refraction are present as the sample is investigated along different axes. In general, it can be very difficult to completely model the effects an anisotropic sample has on beam polarization and/or intensity.
Known patents relevant to Back Surface Reflections are:                Patent to He et al., U.S. Pat. No. 5,963,327;        Patent to Johs, U.S. Pat. No. 5,929,993;        Patent to Synowicki, U.S. Pat. No. 6,738,139;        Patent to Johs et al. U.S. Pat. No. 5,936,734;        Patent to Herzinger et al. U.S. Pat. No. 6,455,853.Other patents and Published Applications which were cited in Parent application Ser. No. 11/452,483 are:        U.S. Pat. No. 5,917,594;        U.S. Pat. No. 6,323,946;        U.S. Pat. No. 6,583,877;        U.S. Pat. No. 5,608,526;        U.S. Pat. No. 5,910,842;        U.S. Pat. No. 6,734,967;        Patent Application No. US 2002/030813;        Patent Application No. US 2004/008349;        Patent Application No. US 2004/100632;        Patent Application No. US 2005/105090.        
Known Articles are:                “Surface Modification of Poly(ethylene terphthalata) Polymeric Films for Flexible Electronics Applications”; Laskarakis et al., Thin Solid Films, 516, (2008) 1443-1448.        “Diffraction for Anisotropic Random Rough Surfaces”; Zhao et al., Phys. Rev. B, Vol. 58, No. 11, 15 Sep. 1998.        “Suppression of Backside Reflections From Transparent Substrates”; Synowicki, Phys. Stat Sol. No. 5, 1085-1088, online Mar. 18, 2008.        “Engineering Properties of High Refractive Index Optical Gels for Photonic Device Applications”; Stone and Connor, Micro and Nano-photonic Materials and Devices, San Jose, Calif., 2000, Proc. SPIE, 3937, 144-155, (2000).        “On the Frustration of Back-surface Reflection from Transparent Substrates in Ellipsometry”; Hayton and Jenkins, Meas. Sci. Technol, 15, N17-N20 (2004), which describes suppression of back-surface reflections from a glass substrate by application of a soft, pliable semi-solid putty to the back side of said glass substrate. While relevant, this article does not disclose application to anisotropic samples but rather the glass substrate investigated was isotropic.        
Need remains for a system which reduces the effect of reflections from the opposite, back, side of an anisotropic sample when electromagnetic radiation is caused to impinge on an incident, front, side thereof, at an oblique or normal angle of incidence, and improved methodology of investigating said samples.